This invention relates to a method of and apparatus for metering liquid samples.
When it is desired to successively process a large number of liquid samples with precise volumetric metering, the parts involved in the metering operation and the passageways communicating with these parts need to be rinsed.
Generally, the cleaning of the flow circuit for the samples is carried out with a rinsing liquid which washes this circuit after the metering of successive samples so as to remove any residues from the previously processed sample.
Unless this precaution is taken, such residues may modify the characteristics of the following sample such as its composition or its concentration, which could result in errors in the analysis.
Apart from the risk that the rinsing operation may modify the concentration of the samples, since there is always a residual quantity of rinsing liquid in the flow circuit, it must also be noted that specific members are needed to perform this operation and the time needed to handle each sample is increased because during cleaning no metering can be carried out.
In an earlier more elaborate proposal for carrying out the general idea set out above (see US-A-4 457 184), there is described a method of collecting samples in which a pipette is rinsed with a rinsing liquid, a given quantity of air is then sucked into the pipette, whereupon a given quantity of sample is sucked in. The sample is thus separated from the rinsing liquid by an air bubble. This technique is delicate and always requires a rinsing liquid.